L3 Flashcards
What is the central dogma (basic)?
Fundamental framework which describes the flow of genetic information within a biological system
What is the central dogma (complex)?
Outlines the processes by which genetic information is transferred from DNA to RNA and then to protein. It begins with transcription, where a segment of DNA is used as a template to synthesise messenger RNA. During translation, ribosomes read the mRNA seq and synthesise a corresponding protein by linking together specific amino acids in order dictated by the mRNA. This process is crucial because proteins are essential for virtually all cellular functions, from structural roles to catalysing biochemical reactions. The central dogma emphasises the directional flow of information : DNA -> RNA -> protein.
What is the gene?
Functional unit of genetic info
What are genes part of?
Genetic elements - large molecules and/or chromosomes.
What is a genome?
All genetic elements.
What is DNA and RNA?
Deoxyribonucleic acid (genetic blueprint), ribonucleic acid (transcription product).
What is mRNA translated into?
Protein
What are information macromolecules?
Nucleic acids and proteins.
What are nucleotides?
Nucleic acid monomers. DNA and RNA are polynucleotides. Nucleotides consist of a pentose sugar, nitrogenous base and phosphate.
What can the nitrogenous bases in nucleotides be? And what can they be?
Adenine - Purine in DNA + RNA
Guanine - purine in DNA + RNA
Cytosine - pyrimidine in DNA + RNA
Thymine - pyrimidine in DNA
Uridine - pyrimidine in RNA
What is the genetic code?
Set of rules by which info is encoded within DNA or RNA sequences is translated into proteins by living cells. It is universal, consists of three nucleotides, known as codons, which correspond to a specific amino acid or stop signal during protein synthesis. There are 64 possible codons, but only 20 amino acids. So the genetic code is redundant as several codons can code for the amino acid. This serves as a protective mechanism against mutations. As changes in DNA seq may not affect protein produced.
What introduces genetic diversity?
Genetic exchange - process by which genetic material is transferred between organisms or exchanged between different parts of the genome within an organism. This introduces genetic diversity which is essential for evolution, adaptation and survival.
What are the mechanisms by which genetic exchange can occur?
Vertical gene transfer, horizontal gene transfer
What happens in vertical gene transfer?
Transmission of genetic material from parent to offspring during sexual or asexual reproduction. Genetic exchange between eukaryotes occurs when two gametes fuse together, and homologous chromosomes exchange genetic information.
What happens in horizontal gene transfer?
Process by which organism transfer genetic material to another organism that is not its offspring. HGT allows for the direct exchange of genes between organisms, often across different species. Common in bacteria and plays a significant role in evolution. Consists of three parts - transformation, conjugation, transduction
How does transformation happen in HGT?
Prokaryote uptakes DNA from the environment and recombines it into its own genome. Cells that could take up DNA from the environment are competent cells. Genetic competence is a transient state that depends on the cells physiological state. Some cells are naturally competent, cells can also be made competent in the laboratory. Some gram-positive bacteria - b subtilis. Some gram-negative bacteria - azotobacter agilis.
How was natural transformation discovered?
Griffith noticed that streptococcus pneumoniae capsule bearing strains killed mice whilst capsule free did not. Capsule made of polysaccharides/amino acids. Helps microbes adhere and form biofilms. Prevents microbes from being eaten up by WBCs. Protects against phagocytosis. With capsule colonies smooth without rough.
What are the conclusions from Griffith experiment?
Heat-killed virulent bacteria could transform non-virulent bacteria into a virulent form. Genetic information can be transferred between organisms.
What is the molecular mechanism behind natural transformation?
Exogenous double stranded DNA binds to proteins of the competent system in the cell membrane. The dsDNA is fragmented into smaller pieces. One strand of the dsDNA is degraded by a nuclease while the other strand enters the cells. The strand in the cytoplasm is coated by transformation-specific DNA-binding protein, protecting inserted DNA from degradation by nucleases in the cytoplasm. If the strand is homologous to an existing region of the cell, the strand gets integrated in the chromosome. Reva invades the homologous region in the cell chromosome, displacing one of the existing strands and replacing it with the new DNA.
What is gene cloning?
Recombinant DNA is introduced in cells artificially.
How is DNA introduced into bacteria?
Chemically competent cells and the heat shock method, electrocompetent cells and an electroporator.
What happens with chemically competent cells and the heat shock method?
Cells treated with chemicals that alter the cell membrane permeability facilitating DNA uptake. Ca2+ ions attracted to negatively charged DNA and negatively charged cell membrane.
What happens with electrocompetent cells and electroporation?
Introduce the gene to the cell, apply the electric pulse ; pores form in the cell membrane and the gene enters. After the electrical pulse, the pores reseal and the gene remains in the cell.
What happens in conjugation in HGT?
Genetic exchange among microbes based on the ability of certain plasmids to transfer from cell to cell. Conjugation can be responsible for rapid spread of antibiotic resustance
How does conjugation work in gram-negative bacteria?
Sex Pilus of the donor bacterium (F+) attaches to the recipient bacterium (F-) (F = fertility). Sex pilis retracts dragging the cells together. A single strand of the plasmid is cut and unwound, and the DNA is transferred to the recipient cell while the donor plasmid creates a new second strand. Once in the recipient cell a second strand is replicated in the recipient cell where it becomes the new (F+) donor cell.
What happens in recombination events?
Very rarely the conjugative plasmid (F factor) can get integrated into the chromosome of the donor bacteria by site-specific recombination. These cells are called Hfr (High-frequency recombination cells). Regions within the plasmid sequence and the chromosome where the plasmid integrate must be similar.
What does site-specific recombination require?
Specific DNA sequences, occurs between the circular and linear DNAs at specific sequences. Two DNA partners. A specialised recombinase protein that is reponsible for recognising the sites and breaking and rejoining the DNA.
What happens in site-specific recombination?
Once integrated the Hfr cell now contains the F factor and can produce sex Pili. The Hfr cell connects with the donor cell and genes in the chromosome of the donor cell are transmitted to the recipient. The length of time of attachment defines how much DNA is transferred. Once in the donor cell the DNA fragment integrates by homologous recombination in the chromosome of the recipient cell.
What happens in homologous recombination?
Donor DNA recombines within the recipients chromosome via at areas of similar or identical sequence. Double crossover inserts the donor DNA into the recipients chromosome.
What happens in conjugation amount gram-positive bacteria?
Similar to gram-negative. Differences is the mechanism that establish cell-cell contact in order to initiate conjugal transfer. Gram-positive bacteria clump together to bring the donor and recipient close. Gram-positive do not form sex Pili.
What is quorum sensing in conjugation?
Some gram-positive bacteria produce pheromones to attract the plasmid of the donor cell
What happens in quorum sensing in conjugation?
Recipient cell produces a pheromone (cA) that interacts with a plasmid (pA) in the donor cell. Plasmid in the donor cell encodes for genes producing aggregation substances (AS). AS migrate to the cell surface of the donor cell. AS bind binding substances (BS) on the surface of the recipient cell. Cells clump together and genetic exchange occurs.
What happens in transduction in HGT?
Transfer of genetic material by a virus. When phages pack their DNA during assembly, they also take DNA from one host to another. Two different kinds of mistakes - phages randomly pack and exchange any of the hosts genes (generalised transduction). Phages only pack and exchange specific genes from the host (specialised transduction).
What happens in the lytic cycle?
Phage attachment and DNA Infectjon into host cell, phage DNA circularises, synthesis of viral nucleic acids and proteins and assembly of new virions. Cell lyses with release of phage virions.
What happens in the lysogenic cycle?
Phage DNA circularises, integration of viral DNA into the bacterial chromosome, lysogenic bacterium can grow normally, on occasion, the prophage excises from the chromosome to initiate a lytic cycle.
How does generalised transduction occur during the lytic phase?
Phage injects its DNA. Phage enzymes degrade host DNA. Cell synthesises new phages, that incorporate phage DNA and, mistakenly, some host DNA. Transducing phage injects donor DNA, donor DNA is incorporated into recipients chromosome by recombination.
How does specialised transduction occur during the lysogenic phase?
Phage DNA is integrated into the bacterial chromosome as a prophage, normal phage excision produces a circular phage again. Abnormal excision results in some of the neighbouring bacterial DNA being carried over in the circular phage while some DNA phage is left behind in the bacterial chromosome.
What can specialised transduction result in bacteria being?
More virulent as it acquires new genes. Less virulent as random integration can damaged normal gene function.
What happens to bacteria after infection with a lytic phage?
Bacterial chromosomes are degraded, cells are being lyses and bacteria killed. Practical application
What are the uses of bacteriophages?
Detect bacteria causing food-borne disease.
